The present invention relates to passivating compositions and a process for treating metal substrates prior to the application of a decorative or protective coating.
Passivating metal substrates with a phosphate conversion coating and chrome-containing rinse, prior to the application of a protective or decorative coating, is well known for promoting corrosion resistance. Phosphate conversion coating compositions typically contain heavy metals such as nickel and post-rinses contain chrome, producing waste streams that pose environmental concerns and which are expensive to dispose.
Rinsing compositions utilizing metal ions other than chromium are also known in the art and are disclosed, for example, in U.S. Pat. Nos. 3,966,502 and 4,132,572. U.S. Pat. No. 3,966,502 discloses treatment of phosphated metals with zirconium-containing rinse solutions. Other rinse compositions containing combinations of Group IVB metal ions with polymeric materials have also been used over phosphated substrates. See, for example, U.S. Pat. Nos. 3,912,548, 5,209,788, and 5,653,823. However, many post-rinse compositions are suitable for use over a limited number of substrates or over substrates that must be phosphated first.
It would be desirable to provide a composition for passivating metal substrates prior to the application of a protective or decorative coating which is substantially free of chrome. Preferably the composition would be effective in passivating a number of metal substrates, particularly metallic objects fashioned with more than one substrate type, such as are commonly found on automobile bodies, so that the need to perform separate passivating treatments would be eliminated. More preferably, the compositions would additionally be effective in passivating untreated (i.e. non-phosphated) metal substrates.